Powdered ceramic raw materials and other inorganic powdered materials are often shipped great distances in bulk. During such transportation, the powder agglomerates and often the agglomerates become compacted. In addition, ambient conditions, i.e. the humidity in the air, contribute to the agglomeration. Once the bulk "powders" reach their destination, there is typically a need for the powders to exhibit good dry flow characteristics so that they can be transferred to different receptacles for storage until such time as they are to be used.
In addition, the key to making high quality homogeneously filled materials is to have a high density with aluminum hydroxide particles as nearly perfectly packed as practical. Attaining such a high density requires an excellent dispersion of the particles in the slurry, polymer resin or resin slurry from which the article is formed.
One can only obtain maximum article density by having optimum packing of particles. To obtain optimum packing one must use particles with as narrow a size distribution as possible and not allow them to agglomerate. To prevent agglomeration, the dispersant generates repulsion between adjacent particles. Such repulsion is provided by a mechanism referred to as "charge stabilization". An alternative is to provide "steric stabilization" by which polymers attach to particle surfaces forming "clouds" around the particles. When particles approach each other, the overlap of the polymer cloud provides an osmotic pressure which keeps the particles apart.
In the past, various organic materials, such as fish oil, have been added to slips and slurries to deflocculate them and thus change their viscosity. In copending U.S. Ser. No. 07/851,610, now U.S. Pat. No. 5,252,655, a hydrolyzed siloxane was used as an addition to a ceramic slurry used to make green tape for the production of multilayer ceramic packages. The teaching of U.S. Ser. No. 07/851,610 is incorporated herein by reference.
Similarly, when the inorganic powdered material is to be used as a filler in a plastic or polymer system, the properties of the resulting product are improved if the particles forming the powder are uniformly dispersed in the product.
The primary object of the present invention is to provide a new method for reducing the agglomeration of ceramic and inorganic powdered materials.
Another objective of the present invention is to provide coated particles which do not require deflocculation after the ceramic particles have been added to slips or slurries.
Another objective of the present invention is to provide a coated particle which exhibits improved dry flow characteristics.
Still another objective of the present invention is to provide a coated particle which has increased sedimentation density and dispersability in aqueous slurries and polymeric resins.
These and other objects and advantages of the present invention will be more fully understood and appreciated with reference to the following description.